1. Field of the Invention
The present invention relates to a printing head for applying an electric image signal to a printing medium.
2. Description of the Related Art
In a conventional electric printing method an electric image signal is changed into heat to melt an ink layer and transfer it to paper to form an image thereon.
One conventional printing head for such a method, shown in FIG. 2, comprises printing electrodes 2 and return electrodes 6. Each of the latter has a larger contact area than each printing electrode, and the electrodes are integral with each other, as disclosed in the Japanese Patent Application (OPI) No. 171666/84 (the term "OPI" as used herein means an "unexamined published application"). Since the recording electrodes 2 and the return electrodes 6 are both present on a surface which is put into contact with a printing medium, the pressure contact area of the printing head is large. For that reason, the total contact pressure of the printing head needs to be high, the surface is less likely to be put in contact with the printing medium with a uniform pressure, and the required torque of a drive roller is large. As a result, the reliability of printing performed with the printing head is low.
In another conventional printing head for such a method, shown in FIG. 3, recording electrodes 2 made of metal layers in a pattern and a ceramic layer 8 are provided on a ceramic board 7. Since the end face of the printing head needs to be put in surface contact with a printing medium to print an image, the area of the contact surface becomes very small if the printing head inclines relative to the printing medium. For that reason, the printing head needs to be always kept vertical by using a head holding mechanism of high accuracy.
The present invention was made in order to eliminate the above-mentioned drawbacks of such conventional printing heads.
Accordingly, it is an object of the present invention to provide a printing head, in which the reliability of contact of electrodes with a printing medium is high so that the electrodes can be put in sufficient contact with the printing medium even under low pressure. Further objects are to provide a printing head having a long service life and high processing accuracy.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the appended claims.